Endogenous methylarginines NGNG dimethyl-L-arginine (ADMA) and NG monomethyl-L-arginine (L-NMMA) which are released by proteolysis of methylated protein arginine residues, are inhibitors of all nitric oxide synthase (NOS) isoforms. The enzyme dimethylarginine dimethylaminohydrolase (DDAH) metabolises the two NOS-inhibiting methylarginines, but not the related NGN′G dimethylarginine (SDMA) which is physiologically inactive.
Thus DDAH, which controls levels of asymmetrically methylated arginine derivatives, may have therapeutic potential through its ability to indirectly influence the activity of NOS.